1. Field of the Invention
The present invention relates to a method of sensing an abnormality in a degassing flow path of a vacuum die casting machine and a system therefore, and more particularly to a method of sensing an obstruction in pipes and filters comprising the degassing flow path of the die casting machine and a system therefore.
2. Description of the Related Art
FIG. 4 shows a schematic arrangement of a system of the conventional vacuum die casting machine. A movable mold part 1 is linearly movable to and from a stationary mold part 2 by a drive device, not shown. When the movable mold part 1 and the stationary mold part 2 are abutted against each other, a cavity 6 is defined. An injection sleeve 3 communicates with the cavity 6 and is connected to the stationary mold part 2. An injection plunger 4 driven by an injection cylinder device 5, for injecting molten metal into the cavity 6 is provided in the injection sleeve 3. In a degassing hole 7 formed between the mold parts 1 and 2, there is provided a vacuum valve device 8 so as to be communicated with the cavity 6. This vacuum valve device 8 functions such that the device 8 discharges gas in the cavity 6 prior to injection of the molten metal into the cavity 6 and closes at the time of injection of the molten metal. The vacuum valve device 8 comprises an on-off valve 9 provided in the degassing hole 7 and a cylinder 10 for linearly moving the on-off valve 9. The cylinder 10 is adapted to be driven by the switching action between a solenoid 11A and a solenoid 11B of a solenoid valve 11. The switching action between the solenoids 11A and 11B in the solenoid valve 11 is controlled in response to output signals of first and second limit switches 13 and 14 which are engaged with a dog (not shown) provided on the injection plunger 4. More specifically, in response to the output signal from the first limit switch 13 when the first limit switch 13 is engaged with the dog, the solenoid 11A is operated to open the on-off valve 9 for preparation of degassing the gas in the cavity 6. On the other hand, in response to the output signal from the second limit switch 14 when the second limit switch 14 is engaged with the dog, the solenoid 11B is operated to close the on-off valve 9, so that the molten metal is injected into the cavity 6 in this state.
A vacuum pump 22 is connected to the vacuum valve device 8 through pipes 20 and 21. The gas in the cavity 6 discharged through the vacuum valve device 8 is discharged by the vacuum pump 22. In the intermediate portions of the pipes 20 and 21, which connect the vacuum valve device 8 and the vacuum pump 22, there are provided a filter 23, a solenoid valve 24, a tank 25 and a solenoid valve 26. Here, the pipes 20, 21, the vacuum pump 22, the solenoid valves 24, 26, the tank 25 and the like comprise a vacuum system.
A solenoid valve 27 is branched from a portion between the solenoid valve 26 and the vacuum pump 22. In response to a pressure detected by a pressure switch 28 secured to the tank 25, the solenoid valve 27 is operated to control the degree of vacuum in the pipes 20 and 21.
However, in the degassing system in the conventional vacuum die casting machine, degassing of the gas from the cavity is intermittently performed under predetermined operating conditions, and a cast product is molded in this state, thus presenting the following problems.
More specifically, in accordance with a predetermined casting cycle, the vacuum valve device 8, the vacuum pump 22 and the like are operated so that degassing of the gas from the cavity 6 can be performed. However, even if changes with time occur in the degassing state as the casting cycle proceeds, these changes cannot be sensed.
Accordingly, when clogging occurs in the pipes 20, 21 or the like which comprise the degassing flow path, a predetermined degassing cannot be achieved. Since the cause and effect relationship between the degassing accuracy and the quality of the cast product is strong, resulting in considerable variations in the characteristics of the cast products thus obtained. As a result, occurrence of a multiplicity of defects cannot be avoided.